1. Field of the Invention
The present invention relates to the field of test devices and, more specifically, an apparatus for testing damping elements of moving blades. The invention employs a mounting means attached to an oscillating apparatus, in which at least two blades are mounted, and a damping element which is to be tested is arranged between the mounting means and the blades.
2. Description of the Related Art
Damping elements are used to eliminate undesired vibration in rotating components of turbines, such as the turbine moving blades. Because the moving blades are almost optimized with respect to material and shape, the use of damping elements is required given excessively high vibration of the blade sheets, which oscillate during operation. Experiments have shown that the damping elements, generally made of steel, effectively reduce the amplitude of the oscillating blade sheets by converting the energy into friction, whereby a frequency shift occurs.
Due to the expensive and costly assembly and measurement processes, it has proven disadvantageous to carry out the experiments for the design of the damping elements on a rotating, or actual system. In addition, the scattering of the measurement values of the individual blade sheets of a system is large, so that corresponding measurement results for a single test provide limited information.
In the design of damping elements, it is thus useful first to carry out preliminary experiments on a static system. In such preliminary experiments, at least two blade sheets are mounted in a test apparatus. These sheets are excited into oscillation by means of an oscillation apparatus, or respectively, a vibrating table, in which the test apparatus is fastened. In contrast to the rotating system, the frequency to be tested of the blade sheets can be set precisely, and the amplitude of vibration can be measured precisely with lasers for example. The measurement results that can be obtained supply specific information concerning the movement of the blade sheets, and form the foundation of a first design for the damping elements according to their mass and rigidity. The damping elements optimized in this way are subsequently subjected to final examination under conditions of actual operation in a rotating system.
However, in the preliminary experiments in the static system, problems arise in the simulation of the centrifugal force. In known testing apparatuses, for this purpose wires are fastened to the damping element to be tested, which is clamped between the moving blades and the mounting means. A tensile force is applied to the wires via a connection and a weight. The resultant force presses the damping elements against the moving blades and away from the testing apparatus. The forces that simulate the centrifugal force are thereby applied only at specific contact points to the damping element, and do not correspond to the actual operating conditions. In addition, the quality of the measurement results suffers from errors inherent in the expensive mechanical system.
Accordingly, one underlying object of the present invention is to create a testing apparatus of the above species, with which the centrifugal forces can be set as precisely as possible and one which can simulate conditions of use as closely as possible in the static system for the design of damping elements.